1. Field of the Invention
This invention relates generally to a photographic exposure control system with a dual purpose light sensing arrangement and, more particularly, to a photographic exposure control system utilizing a single photocell and light emitting diode pair to provide control signals indicative of both objective lens focal position and shutter blade first light.
2. Description of the Prior Art
Photographic camera apparatus embodying shutter blade mechanisms of the scanning type as well as rotatable lens mechanisms which may be automatically focused in accordance with the determined camera-to-subject range are well known in the art and described in U.S. Pat. No. 4,192,587, entitled "Proportional Fill Flash", by A. G. LaRocque et al., issued Mar. 11, 1980, in common assignment herewith and now incorporated by reference herein. Such scanning shutter blade mechanisms are generally spring driven from a scene light blocking position toward a maximum aperture defining position and thereafter returned to the scene light blocking position upon energization of a solenoid. Such scanning shutter blade mechanisms generally comprise a pair of scanning shutter blade elements each having a primary aperture therethrough. The shutter blade elements overlap for reciprocal movement with respect to each other. This movement drives the primary apertures into overlapping relationship with each other so as to define a progressively increasing effective primary aperture. In the course of this displacement the shutter blade elements are driven through a position where the primary apertures in each blade first begin to overlap to allow the initial transmission of scene light to the camera focal plane. The instant that the scanning shutter blades reach the so-called first light position is important to determine accurately since other exposure influencing events such as the firing of an electronic flash are timed from that instant in a manner as is fully described in U.S. Pat. No. 4,192,587, supra.
Auto focus cameras of the aforementioned type generally embody a rotatably driven objective lens mechanism which must be stopped at an appropriate focal position corresponding to a previously determined camera-to-subject distance. In such systems it is desirable to provide a positive feedback signal to identify the instantaneous focal position of the lens mechanism as it is rotated through its plurality of different focal positions so that it may be stopped at the appropriate focal position corresponding to the determined camera-to-subject distance range.
Therefore, it is a primary object of this invention to provide a simple and economical light sensing arrangement for serving the dual purpose of sensing both the focal position of the objective lens mechanism and the first light position of the shutter blades.
It is a further object of this invention to provide a dual purpose light sensing arrangement comprising a single photocell and light emitting diode to provide control signals which are indicative of both the objective lens focal position and the shutter blade first light position.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure.